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====== CS102 Lab03 - Get into Shape ====== Design, implement and explore simple class hierarchies, abstract classes and interfaces. //Note//: This assignment has nothing to do with drawing graphics in Java, everything is done on the console as usual! Create one JCreator project for part (1) and another for part (2), both within the same workspace. - **Shape up** * Design a class hierarchy to include classes ''Shape'', ''Rectangle'' (with ''width'' and ''height''), ''Circle'' (with ''int radius'') and ''Square'' (with ''int side''). ''Shape'' should be abstract with method ''double getArea()'' and ''Square'' should inherit ''getArea()'' from ''Rectangle''. * Create another class, ''ShapeContainer'', to hold a set of shapes. It should have methods ''void add(Shape s)'', ''double getArea()'', and ''String toString()''. * Write a ''ShapeTester'' class with a menu that allows the user to: * create an empty set of shapes (''ShapeContainer''), * add as many circle and rectangle shapes to it as they wish, * compute & print out the total surface area of the entire set of shapes, and * print out information about all of the shapes in the container by calling the ''toString()'' method for each shape. * //Experiment//. Try to predict what would happen when you (i) comment out the ''getArea()'' method of the ''Circle'' class, and (ii) also make the ''Circle'' class abstract, before finally (iii) creating an instance of the (now abstract) ''Circle'' class to add to the shapes collection. Test your predictions. * **[New for Lab3ext]** The customer is impressed with your work so far, and so asks you to extend the program. They want ''Shapes'' to be locatable (i.e., to have an ''x'', ''y'' location, and ''getX()'', ''getY()'' and ''setLocation(x, y)'' methods). As a good designer you decide to first create a ''Locatable'' interface with these methods, then have the ''Shape'' class implement it. In this way all shapes automatically become locatable. Add new options to your ''ShapeTester'' menu that allows the user to set the locations for shapes. Update the ''toString'' method to show the location of shapes. * **[New for Lab3ext]** The customer further asks you to add a method ''move(dx, dy)'' in order to move a shape ''dx'' units on the ''x''-axis and ''dy'' unit on the ''y''-axis. Create a ''Movable'' interface to implement this. Add a new option to your ''ShapeTester'' menu that allows the user to move shapes. * **[New for Lab3ext]** Impressed, the customer wants even more! This time they ask for shapes to be ''Selectable'', so you again start by creating a Java interface, having ''boolean getSelected()'' and ''void setSelected(boolean)'' and ''boolean contains(int x, int y)''. Unfortunately, this time--for some unknown reason--you are not allowed to change the ''Shape'' class. Modify your other classes so that each shape added to the ''ShapeContainer'' is ''Selectable''. Change the ''toString()'' methods so that they show whether the shape is selected or not. Add another option to your ''ShapeTester'' menu that allows the user to find the first ''Shape'' that contains a given ''x'', ''y'' point and toggle its selected state. Provide another menu option that removes all selected shapes from the set of shapes. -- **Iterating ''IntBag''s** * The Java API includes an interface called ''Iterator'' that is designed to retrieve each of the objects from a set of objects, once and once only. This allows programs to process each item in the set without being aware of the underlying implementation (which means it can be changed at will without affecting the client program). Your task is to provide this interface for your ''IntBag'' class. * //Note//: The ''IntBag'' class was designed to store primitive ''int'' types, rather than Java ''Object'' types. Since the ''Iterator next()'' method must return an ''Object'', you will need to return the corresponding ''int'' in an ''Integer'' wrapper. Clearly, this is not an entirely satisfactory solution and you might consider extending ''Iterator'' to produce ''IntIterator'', which provides an additional ''int nextInt()'' method. * There are several ways you might think of coding this problem. Clearly you must have a value (say index) that keeps track of position of the next item to be retrieved from the ''IntBag'' collection. This must be initialized to zero when an iteration begins, and be incremented each time a call is made to get the next element (such call returning the element at the index location within the set.) The ''hasNext()'' method simply determines whether the index value is less than the number of elements in the set or not. Putting this code inside the ''IntBag'' class is problematic; how can index be reset to zero so that the elements can be iterated through several times, and how can multiple independent iterations through the set be managed? * A simple solution to this is to write a new class, say, ''IntBagIterator'', which implements ''Iterator''. This class need have only two properties; ''bag'' (a reference to the ''IntBag'' set it is to iterate through) and ''index'' (the position of the next element to return from the bag). Code this class. * Test it using a class, ''TestIterators'', which contains the following code, <code> Iterator i = new IntBagIterator(bag); while (i.hasNext()) { System.out.println(i.next()); Iterator j = new IntBagIterator(bag); // Iterator j = bag.iterator(); while (j.hasNext()) System.out.println("--"+j.next()); } </code> * Notice that ''i'' and ''j'' are of the interface type, ''Iterator''. This is valid since ''IntBagIterator'' implements ''Iterator'' and so is an ''Iterator''. * Finally, add a method ''Iterator iterator()'' to your ''IntBag'' class. This should create an instance of ''IntBagIterator'' and return it as the interface type. Test this method by uncommenting the commented line in the above code and commenting out the line above it. * Java's ''ArrayList'' class has a similar method that allows you to iterate through its elements. Interestingly, there is no (immediately obvious) class in the Java API that corresponds to our ''IntBagIterator'' class. It actually has such a class, but nested inside ''ArrayList''. The curious might like to read up on nested classes and perhaps even examine the Java source code for the ''ArrayList'' class to see how they did it!